Secrecy telefacsimile system



July 2, 1946. 2,403,059

G. VAN DER V. DILLENBACK. JR., ETAL SECRECY TELEFACSIMILE SYSTEM Filedlly 11, 1940 j /a /f 7 E np e Y mcs/m mcs/Mu. E AH II MP /7 I T2AMsn/Tree M00- ,d enf/rie Y FAcs/M/L E A E m Faas/NLE nemen/rma ?2/ 0R yDH1 v ,j fief/ 14? W Z f :LL-. E. Z f7 f7 TEAMS INVENTOR 20 BY /L Tf' l1? x ceiver.

PatentedfJuly 2,1946

sEcREoY TELEFAcslMmE SYSTEM Garett Van der Veer Dilienback, Jr.,Slingerlands,

and Austin G. Cooley,Hudson View Gardens, N. Y., assignors, by mesneassignments, toATimes Telephoto Equipment Inc., New York, N. Y., a

corporation of New York Application May 11, 1940, Serial No. 334,516

18 Claims. 1

'I'his invention relates to telefacsimile systems and more particularlyto methods and means for transmitting and receiving facsimile subjectmatter or the like with secrecy.

A principal object of the invention is to provide method and means forpractically preventing synchronism of an unauthorized receiver with atransmitter.

Another object is to provide methods and means for maintaining secrecyin a signaling systern wherein the receiving means is provided with asynchronizer device which is adapted to be operated under .control ofreceived synchronizing signals. d

Another object is to provide methods and means for maintaining secrecyin a. telefacsimile system or the like wherein synchronization of thereceiver and transmitter is eiected by an inherent frequency componentof the transmitted facsimile signal.

A feature of the invention relates to an improved secrecy telefacsimilesystem employing a modulated audio frequency carrier for the signals.

Another feature relates to the means for transmitting simultaneouslywith a desired synchronizing signal, one or more arbitrarily chosen`frequencies having no readily determinable relation l to thesynchronizing frequency.

A further feature relates to the means for transmitting simultaneouslywith a desired synchronizing signal, one or more arbitrarily chosenfrequencies which can be independently varied during transmission of themessage without affecting the synchronization of an authorized re- Astill further feature relates to the novel organization, arrangement andrelative interconnection of parts which cooperate to form an improvedsecrecy signal transmission system especially suitable for facsimiletransmitters and the like.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.

In the drawing which shows by way ofexample several embodiments of theinvention, j

Fig. 1 is a schematic diagram of a telefacsimiie system according to theinvention.

Fig. 2 is a modification pf Fig. 1.

Fig. 3 is a mo'dication of Fig. 2.

Fig. 4 is a schematic view of one typical form of random couplingaccording to the invention.

Fig. 5 is a schematic diagram of a modification of the, invention. A

Inasmuch as telefacsimile systems and apparatus are well-known, onlythose parts which are necessary to an understanding of the invention areillustrated in the drawing. While the invention will be described asapplied to certain types of signaling systems, it will beiunderstoodthat the inventive concept can be equally well applied to other types ofsignaling systems. The invention may be embodied `in a system of thetype wherein the telefacsimile signals or other message signalsthemselves. are -used as a synchronizing control to maintain a receiverin synchronlsm with a transmitter. Such a system is disclosed in PatentNo. 2,015,742 to Austin G. Cooley.

-Referring to Fig. 1 of .the drawing, the block I representsschematicallyv any well-knownform of facsimile transmitting machineusually comprising arotatable drum around which is wrapped the subjectmatter to be transmitted. This subject matter is arranged to be scannedin successive elemental areas to produce corresponding electric currentsasis well-known in the art andas described for example in said PatentNo. 2,015,742. There is provided a motor 2 which' drives the scanningmechanism of machine I through suitable gearing 3. The facsimile'signals from machine I. usually in the form of relatively low frequencycurrent variations, are impressed upon a suitable amplifier modulator 4.

Modulator l is also supplied with an audio frequency carrier undercontrol of a generator vIi. Preferably, this generator consists of atoothed `magnetic rotor '6 fastened to shaft 'I which is driven at therequired speed by 'motor 2. Associated with rotor B is a magnetic polemember v8 v having an energizable or pick-up winding 9 which isconnected to the modulator 4. Consequently,

the output of modulator l will consist of a'carrier wave determined bydevice 5, the amplitude of the carrier waves being modulated inaccordance with the signals from machine l. lPreferably the generator 5isl such that the rotor 6 can be readily removed and replaced byanother. rotor for purposes to be described.

At the receiving station schematically shown in the right-hand portionof Fig. ,1, the modulated carrier wave received from ythe line ortransmission channel L is amplified in a suitable amplifier I0. theoutput of which-is used to control a reproducing light sourcewor otherAwellknown recording element inthe facsimile receiving machine H. Thereceiving machine may comprise a scanning drum adapted to be rotatedvabout its own axis and advanced bodily along its axis in any well-knownmanner. If desired, the drum may be merely rotated about its own axisand the reproducing light source or the like may be advancedlongitudinally as described in said Patent No. 2,015,742. For a detaileddescription of a typical drum scanning arrangement that may be used,reference may be had to Patent No. 2,138,784 to Austin G. Cooley.

For the purpose of operating the scanning mechanism of machine there isprovided a motor I2 which may be of the induction type and coupledthrough suitable gearing i3 to the scanning mechanism of machine II. Inorder4 to maintain synchronism, the driving shaft I4 has coupled theretoa synchronizing motor |5 comprising a toothed magnetic rotor I6 and amagnetic pole member I1 having an energizing winding I8. Winding I8 isadapted to be energized by part of the received carrier from line Lafter passing through a suitable amplier I9. Preferably the rotor I6 isreadily removable so that it can be replaced with another rotor tocorrespond with a change of rotor 6 at the transmittel'.

Heretofore, where synchronizer devices such as 5 and I5 have beenemployed. the rotors have been designed with the poles or teeth 20equally distributed around the rotor so as to produce a synchronizingsignal wherein all the impulses are of equal duration and are of uniformrecurrence. As an example of such a system reference may be had to U. S.Patent No. 1,590,270. In such prior systems, it is relatively easytherefore for an unauthorized person to pick up the transmittedfacsimile signals and to determine the frequency'of synchronization.This is possible, because in the prior arrangements the synchronizingsignal will be revealed by its regularity and substantially singlefrequency characteristic. In accordance with the present invention, thesynchronizing rotors E and IB are provided with the same number of teethor poles 20, but these teeth are arbitrarily grouped and distributedaround -the rotor. While Fig. 1 shows the rotors with five teeth, two ofwhich are close together and the other three relatively widely spaced,it will be understood that any other number and arbitrary distributionof the teeth around the rotor may be employed, provided the distributionin the transmitting and receiving rotors is substantially identical. Inany event the teeth are so arranged that the spacing between successiveteeth progressively varies around the rotor circumference so thatsynchronism cannot be obtained at a receiver which employs a rotorhaving equally spaced teeth. Preferably the rotor teeth are arranged sothat no regular or uniform teeth spacing occurs over a major part of therotor circumference. In order that the receiving rotor I8 and thetransmitting rotor 6 may correspond as to number and arrangement ofteeth 'they may vboth be cut during the same cutting operation by thesame cutting or punching tool or the like. Thus in the case of laminatedrotors the laminations may all be cut at the same time for both thetransmitting and receiving rotors with the teeth integraltherewith.uniformly spaced teeth rotors vand remove in any suitable manner therequisite number of teeth at arbitrary intervals with the understandingthat the transmitting and receiving rotors are substantially alike. Itwill also be understood If desired however one may start with' 4 if thesame peripheral width or pitch so long as the impulses transmitted bythe transmitter rotor arrive at the receiving rotor in the proper phaserelation with respect to the corresponding teeth on the receiving rotorwhile rotating, that 'the said impulses tend to pull the receiving rotorinto step or to maintain it in step with'the transmitting rotor. When,the rotor I6 at the receiver has substantially the same number andarrangement of teeth as the rotor 6 at the transmitter, the propersynchronism 'is obtained and it is extremely difficult for unauthorizedreceivers to reproduce an intelligible facsimile.

In order to increase the secrecy factor, one or more additional rotorsmay be used at the transmitter so that there are impressed upon the lineor communicating channel L two or more sets of impulses, but only one ofwhich may be used for synchronization. Such an arrangement is shown inFig. 2 wherein the parts similar to those of Fig. 1, bear the samedesignation numerals. In Fig. 2, the'shaft 1 in addition to carrying thetrue synchronizing rotor 6, also carries two other toothed rotors 2|,22, which have their poles or teeth 23, 24, distributed around therespective-rotors in different arbitrary arrangements. the distributionbeing different from the distribution of the teeth on the truesynchronizing rotor 6. Each of the rotors 2|, 22, has associatedtherewith a pick-up arrangement in the form of respective magnetic poles25, 26, and windings 21, 28, which also feed the modulator 4.Consequently, there is impressed upon the line L in addition to the truesynchronizing frequency determined by the rotor 6, other sets ofimpulses determined by the rotors 2| and 22. At the receiver themechanism is provided with .a synchronizing motor I5 having a rotor I6identical with the true synchronizing rotor 6. Consequently, the rotorI6 will respond only to the frequency and distribution of synchronizingimpulses corresponding to rotor 6. The remainder of the system is thesame as that of Fig. 1 and further description thereof is not necessary.However, in order to prevent unauthorized interception and reproduction,the rotors 2| and 22 should be coupled to shaft 1 by some kind ofcoupling having random play therein, so that the currents induced inwindings 21 and 28 will not be of constant frequency or constant4impulse distribution with respect to the scanning rate, but rather ofrandom or fortuitous impulse distribution with respect to time. Onemanner of accomplishing this is to provide a gearing between each of therotors 2l, 22, and shaft 1, which gearing has considerable "play betweenthe meshing teeth. Another way is shown in Fig. 4 wherein the shaft 1has fastened thereto a friction disc 1a upon'which is loosely fitted therotor 2| so that there is a slight clearance b`e tween the rotor 2| andthe driving disc 1a. However, the rotor 2| normally rests on the disc 1aand is rotated by the frictional engagement therewith, and because ofthe slip between the members 1a and 2|, the latter is rotated at afortuitous speed. Other equivalent methods may be used for energizingthe windings 21 and 28 with fortuitous impulses.

As an additional secrecy factor, the rotors 2| and 22 of Fig. 2, may becoupled to the shaft 1 by variable gear transmissions. Such anIarrangement is shown in Fig. v3 wherein the parts correspending tothose of Fig. 2, bear the same designation numerals. In this figure, therotor 2| is that it is not necessary that all the teeth have 78 coupledto the shaft 1 by a manually variable gear ratio 29 of any well-knownconstruction. Likewise, the rotor 22 is coupled to the shaft 'I byanother manually variable gear ratio'30. In this embodiment, the rotors2I and 22 are likewise attached to their respective shaft portion 1 bymeans of a variable frictional coupling such as that shown in Fig 4.Preferably, the gearing arrangements 29 and 30 are such that the speedof rotation of the rotors 2| and 22 may be manually varied at any timeduring the transmission of the message without affecting the speedof'rotation of the true synchronizing rotor 6.

In all the foregoing embodiments, as an additional precaution thescanning drum or other movable scanning element of the transmitter I maybe driven at a variable speed so that received copy will be distorted inscale unless matched gearing is used at transmitter and receiver. Thegearsets may be made readily changeable for altering the coding. Theratio between scanning rate and synchronous rotor speed may be changedat will in the same manner, further complicating the problem ofsynchronizing an unauthorized receiver. Thus the gearing 3 whichconnects the driving motor 2 to the rotatable scanning element of thefacsimile transmitter and also gearing I3 at the receiver, may be of anywell-known variable ratio type, so that the speed of rotation or speedof movement of the scanning element varies from instant to instantaccording to a definite law. Consequently, the Asignals from thephoto-electric cell of the facsimile transmitter will have a varyingscanning frequency and it will notl be possible for an unauthorizedreceiver to determine from these signals the actual speed of thetransmitting scanner element. f course at the receiver, the gearing I3should be correlated with the gearing 3 so that the scanning' drums ormovable scanning elements of the machines I and II are driven at thesame speed at any given instant.

While in the foregoing, specific apparatus has been mentioned, it willbe understood that various changes and modifications :may be 'madetherein without departing from the spirit and scope of the invention.Thus, while the synchronizing impulses are produced by a mechanicallyrotating member 6, it will be understood that any equivalent electricalmeans may be employed for generating the synchronizing impulses incyclically repeated groups but with the individual imrpulses of thegroups arbitrarily spaced. Likewise, while in the systems of Figs. l, 2and 3, the current from the device li is also used as the carrier forthe facsimile signals, it will be understood that the current from thedevice 5 may be applied to the line L as a separate synchronizingsignal. Thus the output of machine I may consist of an audio frequencycarrier having a random carrier. frequency as above mentioned, modulatedin accordance with the lights and shades of the successive elementalareas of the subject matter bepulses corresponding to the facsimilesignals.

ing transmitted. At the same time, the arbitrary synchronizing signalsfrom device 5 are impressed upon the channel L. In such an. arrangementpreferably the signals from the device 5 are di- .stantially uniformamplitude.

Thus as shown in Fig. 5, the `picture current signais from thetransmittermachine I are applied to any well-known form of frequencymodulator 30 whereby the varying amplitude picture signais aretranslated into corresponding'. variable frequency signals whichpreferably are of sub- These frequency modulated signals are transmittedto the receiver and are demodulated in any well-known form of frequencydemodulator 3l, lthe output of which is suitably amplified andv appliedto the recording lamp or other element of machine .II

The synchronizing signals picked up in the winding 9 are applied to anlamplitude modulator 32 and are transmitted over the 'transmissionchannel to an amplitude demodulator 33, the output of which aftersuitable amplification energizes the winding I8 to control the speed ofthe driving motor I2. It will be understood of course that i-n Fig. 5,the vpicture signals and the synchronizing signals instead of beingtransmitted over separate channels may be transmitted over the same lchannel. It will also be understood that in any of the foregoingarrangements, it is not necessary that the picture signals betransmitted in thev form of a modulated audio frequency carrier sincethey may be transmitted directly over `the transmission channel as forexample over a Kcable by D. C. transmission.l Likewise, the output ofmachine I may be used to modulate directly a radio frequency carrier inwhich event thetrlansmission channel will be a suitable radio channel.In this event, the arbitrary synchronizing signals may be transmittedover the same radio channel or -they may be transmitted as an audiofrequency signal over an audio frequency channel.

As another precaution against unauthorized intervention and reception,the main driving motors 2 may be provided with manually variable meansso as to adjust during'trans'missiomthe speed of the various componentsin an arbitrary manner at the. transmitter. However, as a result of thespecial synchronizing arrangements disclosed, the receiving motor .I2will be maintained in synchronism with the arbitrarily varied speedk ofthe driving motor 2 at the transmitter.

'As a nal precaution the subject matter which is being transmitted .maybe prepared-so that it is substantially free from regular'lines or pat.

tems from 'which yan' unauthorized recipient might determine the manualadjustment of thespeed of his Areceiver to correspond withthereghaving'a' signal ltransmitter and a signal receiver 'whichiare Ito bemaintained in motional synchronism, a synchronizing impulse producer atthe transmitter, means 'to rotate said producer to accanto ducer at thetransmitter having a series of impulse producing elements which arespaced to produce impulses with non-uniform time intervals therebetweenwhen the said impulse producer is rotating at substantially uniformspeed, a continuously rotating synchronizing impulse i'esponder at thereceiver having impulse responding elements corresponding in number andspacing to the elements of the said impulse producer, and means totransmit and apply the impulses from said impulse producer to saidimpulse responder, said responder locking itself in synchronism with theproducer only in response to said non-uniformly spaced impulses.

3. Means for synchronizing between signaling devices comprising agenerator for transmitting synchronizing impulses having non-uniformspacing between successive impulses, and a synchronous motor responsiveonly to said non-uniiormly spaced impulses to lock itself in synchronismwith said generator.

i 4. Means for synchronizing between signaling devices comprising agenerator for transmitting synchronizing impulses having non-uniformspacing between successive impulses, and a synchronous motor responsiveonly to said non-uniformly spaced impulses to lock itself in synchronismwith said generator both the generator and motor having toothed rotorswith the same number and non-uniform spacing of poles.

5. 'Ihe method of secret'signaling between a signal transmitter and asignal receiver which are to be operated in synchronism which includesthe steps of generating at the transmitter a secret synchronizing signalin the form of series of impulses having non-uniform impulse spacingstherebetween, locking the receiver into synchronism with the transmitteronly in response to said non-uniformly spaced impulses, transmittingsimultaneously with the synchronizing impulses one or more other seriesof .non-signaling impulses, each of said other series being constitutedof a succession of impulses having non-uniform spacings which spacingsare different from the spacings of the impulses of said synchronizingsignal, at least one of said other series oi' impulses being generatedat a random frequency or impulse distribution with respect to time.

6. The method of secret 'signaling between a signal transmitter and asignal receiver which are to be operated in synchronism which includesthe steps of generating at the transmitter a secret synchronizing signalin the form of series of impulses having non-uniform impulse spacingstherebetween, locking the receiver into synchronism with the transmitteronly in response to said non-uniformly spaced impulses, transmittingsimultaneously with the synchronizing impulses one or more other seriesof non-signaling impulses, each of said other series being constitutedof a succession of impulses having non-uniform spacings which spacingsare different from the spacings of the impulses of said synchronizing 8signal, and varying the rate of generation of said other sets ofimpulses during transmission of the signaling impulses.

7. In a facsimile signaling system, a facsimile transmitter machine, afacsimile receiver machne, each of said machines having members arrangedto be operated in synchronism, an impulse type current generatorassociated with the transmitter for generating cyclically recurringseries of synchronizing impulses with successive impulses of each seriesspaced non-uniformly but with each series having the same number ofimpulses, and an impulse type synchronizing motor associated with thereceiver and responsive to said synchronizing impulses for convertingsaid impulses into corresponding cyclioally recurring series ofelectro-mechanical impulses having the same number and impulse spacingas the nrstmentioned series.

8.- In a facsimile signaling system, a facsimile transmitter machine, afacsimile receiver'machine, a rotatable impulse generatcr'associatedwith said transmitter, a synchronous motor associated with saidreceiver, saidimpulse generator arranged to generate recurring series ofimpulses with successive impulses spaced non-uniformly but with eachseries having the same number of impulses, and said synchronous motorhaving its stator and rotor designed so that it runs in synchronism withsaid generator onlywhen it receives said impulses oi' non-uniformspacing.

9. In a signaling system of the type having a signal transmitter machineand a signal receiver machine to be maintained in secret synchronism,

means to maintain said secret synchronism including a toothed magneticrotor and an associated magnetic stator foreach machine, the teeth onthe transmitting rotor being non-uniformly spaced so as to producesynchronizing impulses with non-uniform spacing therebetween, and theteeth on the receiving rotor being likewise nonuniformly spaced tocorrespond with the spacing on the transmitting rotor, said receivingrotor being locked in synchronism-only in response to the receipt ofsaid non-uniformly spaced synchronizing impulse. l

10. In a signaling system of the type having a signal transmittermachine and a signal receiv..

er machine to be maintained in secret synchronism therewith, means tomaintain said secret synchronism including a rotary inductor at thetransmitter for producing series of impulses with the spacing betweensuccessive impulses non-uniform, and a similar rotary inductor at thereceive arranged to be locked in synchronism with the transmitterinductor only in response to said non-uniformly spaced synchronizingimpulses.

11. A signaling system according to claim 10 in which the rotaryinductor at the transmitter has a toothed rotor with the teeth`non-uniformly spaced, and the rotary inductor at the receiver has atoothed rotor with the teeth non-uniformly spaced and corresponding tothe spacing of the teeth in the transmitting inductor rotor.

12. In a system ofthe character described, a transmitter having a motorfor operating the same to produce message signal impulses, a rotaryinductor driven by said motor for producing cyclically recurring seriesof synchronizing impulses with successive impulses non-uniformly spacedand with each series having the same number of impulses, and at leastone other rotary inductor also driven by said motor and producing non- 9signaling impulses with successive impulses nonuniformly spaced and withthe spacing different from that of the synchronizing impulses.

13. A system according to claim 12 in which said non-signaling impulsesare generated at a random impulse distribution.

14. In a facsimile signaling system a movable scanning member, meanstomove said member in a scanning motion and for varying the speed of saidmember from time to time during scanning, a synchronizing impulsegenerator associated with said scanner for generating synchronizingimpulses in cyclically recurring series with the `impulses havingnon-uniform spacings therebetween but with each serieshaving the samenumber of impulses.

15. In a facsimile signaling system a rotatable scanning drum, a motorfor driving said drum, means between said motor and drum for varying thespeed of the drum from time to time during scanning. a synchronizingimpulse generator locked to the speed oi' said motor and arranged togenerate `synchronizing signals in the form of cyclically recurringseries of eurrentimpulses having non-uniform spacings therebetween butwith each series having they same number of impulses.

16. The method of secret signaling between a.

transmitter and a receiver each of which has elements to be operated insynchronism which inw AUSTIN' G. COOLEY.

10 cludes the steps of transmitting the signals from the transmitter tothe receiver by frequency modulation. secretly synchronizing thetransmitter and the receiver by transmitting secret synchronizingsignals in the i'orm of a series of current impulses having non-uniform.spacings therebetween. and locking the receiver in synchronism with thetransmitter only in response to said non-uniformly spaced impulses. l

17. The method oi secret signaling according to ciaim 16 in which` thesynchronizing signals i are also transmitted by frequency modulation.`

18. In a facsimile signaling system,themethod of synchronizing afacsimile transmitting ma.-

chine with a receiving machine while maintainingsecrecy of transmission,whichincludes the steps of transmitting synchronizing signals be tweenthe machines in the form of cyclically recurring series of currentimpulses with. non-uniform spacings therebetween but with each serieshaving the same number oi impulses, and simul- I taneously transmittingover the Vsame channel as -the synchronizing signals othernon-synchronizing and non-signaling impulses having random -frequencyand non-uniform spacings between impulses which frequency and spacingare dierent from those ofthe synchronizing signal impulses.

GARE'I'T VAN DIR VEER DIILENHBACK, JR.

